# Set matrix element to zero for some condition

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Philipp 2023 年 6 月 1 日
コメント済み: Vilém Frynta 2023 年 6 月 1 日
Hello,
I'm new to Matlab and have a simple question. I have a matrix M of numbers and I like to create a new matrix, where all elements are set to zero that do not satisfy a certain condition (say, e.g., all elements larger than 1). How do I do this in the most efficient way?
I tried
filter = find((M<=1));
Mnew = M(filter);
but unfortunately it doesn't work because filter gives me a list of linear indices, but I like to keep the shape of the matrix M. I know that
[row,col] = find((M<=1));
gives me the row and column indices separately, but
Mnew = M([row,col]);
also does not do the job (I kind of understand that it does not work, but I have no idea how to fix it).
Any help is greatly appreciated!

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### 採用された回答

Vilém Frynta 2023 年 6 月 1 日

Hi,
my approach would be as follows:
% Matrix 5x5 with random numbers 0-10
M = randi(10, 5)
M = 5×5
9 6 4 8 8 2 5 10 7 1 9 7 8 2 7 6 4 3 9 9 6 1 5 8 5
% Create logical vector of numbers higher than 5 (condition)
idx = M > 5;
% Apply it to your matrix and set those values to 0
M(idx) = 0
M = 5×5
0 0 4 0 0 2 5 0 0 1 0 0 0 2 0 0 4 3 0 0 0 1 5 0 5
Ultimately, you can do it in one line.
M(M>5)=0;
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Philipp 2023 年 6 月 1 日
Oh, thanks lot. I expected there was a simple one-line answer, but I was unable to find it! :)
Vilém Frynta 2023 年 6 月 1 日
Yes, in MATLAB, there's always simpler solution to the problem than you have. Almost always when I help people on this forum, someone better comes and does something I recommended much easier.
Happy I helped.

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